1. Field of the Invention
The invention is directed to an ion optical element used for controlling charge particle beams, typically used in mass spectrometers. More particularly, the invention is a volume or surface conductive electrode used to control charged particle beams in time of flight mass spectrometers and other devices requiring precise control of charged particles.
2. Description of the Prior Art
The control and use of charged particle beams is of considerable interest to scientists in a wide range of fields. Chemists, physicists, and biologists have all benefited from the use of these beams to probe new materials, control the momentum of interacting particles and analyze elements within complex mixtures. Imperative to all of these applications is the manipulation of the momentum of charged particles via precisely aligned electrical fields, which are generally created from discrete electrode stacks. Typically, these electrodes are produced from metallic materials e.g., stainless steel. However, researchers have recently begun to use novel, conductive materials to generate electrostatic fields. One of the disciplines that has made use of these new materials is mass spectrometry, particularly time of flight mass spectrometry (TOFMS).
Gruen et.al., “Photo Ion. Spectrometer,” U.S. Pat. No. 4,855,596 teaches the use of a resistive paste screen printed on a substrate to provide for control of charged particle beams in a photo ion spectrometer. This instrument utilized an electrostatic analyzer, which used a curved plate composed of a resistive thick film deposited as paste on an insulator surface. It was reported that screen-printing BIROX (Du Pont), a resistive bismuth-ruthenium oxide compound, deposited on top of a conductive paste allowed the generation of precise electrostatic fields and was ideally suited to the creation of irregularly shaped and non-linear potentials. The use of a resistive paste renders the creation of nonlinear and linear electric field very complicated.
Previous reflectrons consisted of stacks of discrete electrodes. These stacks can be expensive to manufacture and are inherently imperfect, namely the field produced by the assembly or electrodes is not precisely linear. In general, TOF instruments use a series of metal rings (electrodes) connected via bleeder networks of resistors to approximate linear fields. Combinations of these linear fields are then used to generate electrostatic lenses as well as multiple stage ion sources and reflecting devices (reflectrons). Recently, it has been proposed to combine electrodes and resistors in a bulk conductive electrode.
Others have provided an ion source with three acceleration regions was fabricated from alumina ceramic tubes brush coated with a resistive paste. Once coated, the cylinders were air fired to create a vacuum compatible conductive surface. When coupled to a 700 mm long flight tube this linear instrument provided a mass resolution of m/Δm=1200 full width half maximum.
What is needed is a design for an assembly which is inexpensive to manufacture and allows the precise generation of linear and nonlinear fields.